How does the PFD show (calculate) wind velocity during the takeoff roll ?
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Guys, plz. It's not about shear, looking at it or not, what will I do etc BUT
HOW DOES A COMPUTER CALCULATE WIND WHEN AC IS ROLLING DOWN A STRAIGHT RUNWAY WITH NO CRAB?
HOW DOES A COMPUTER CALCULATE WIND WHEN AC IS ROLLING DOWN A STRAIGHT RUNWAY WITH NO CRAB?
aquarium1, quietly now. It may help by specifying the aircraft type, nav fit, and or particular operation.
There are many methods of calculating a wind vector, and even for the same aircraft type in the choice of which one to display; IRS, GPS, smoothed inertial nav, integrated nav position, etc.
I will not be able to provide an answer re on the ground, as my aircraft did not display a vector until the airborne calculation was considered valid.
The answer to a question is often obvious once the problem behind the question is understood.
There are many methods of calculating a wind vector, and even for the same aircraft type in the choice of which one to display; IRS, GPS, smoothed inertial nav, integrated nav position, etc.
I will not be able to provide an answer re on the ground, as my aircraft did not display a vector until the airborne calculation was considered valid.
The answer to a question is often obvious once the problem behind the question is understood.
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From my experience, the wind vector seems to be accurate
A rejected takeoff is a potentially hazardous manoeuvre and the time for decision-making is limited. To minimize the risk of inappropriate decisions to reject a takeoff, many warnings and cautions are inhibited between 80 kt and 1 500 ft.
When even failures are inhibited on take off why should anyone include in the decision making an information he is not even sure of it's authenticity. There is no better situation than take off for keep it simple. If you rejected for ND wind and airbus comes out with it's unsuitability on ground you may find yourself very lonely.
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I must be getting old. In all my years I have only ever been interested in 3 things during the takeoff roll:
1. Runway centreline;
2. IAS; and
3. Engine EGTs.
So, in answer to any question about the wind vector during the takeoff roll, my answer must be "what wind vector?"
The IAS indicator will tell me anything I need to know about windshear. I don't care what the wind is. If the IAS is telling me the aircraft can't fly, then that means stop. If the IAS is telling me I can fly, and there is insufficient runway to stop, then I go. The wind might be 50 knots on the tail. I don't care. Letting a wind vector influence your stop/go judgement is asking for trouble. The aircraft doesn't care about wind, it only cares about IAS. It's IAS that makes you fly (or not), not wind. And it's the EGT's that will keep you flying... There is nothing else in the cockpit that is of any interest during the takeoff roll.
Funnily enough, Boeing don't make any mention of the wind vector in the windshear section of their manuals either. And windshear is not the only potential cause of slow acceleration: sticking brakes or incorrect takeoff data could be other examples. Only your IAS will tell you if you have slow acceleration, regardless of the cause.
So, eyes off the wind vector and back to the IAS/EGTs where they belong please folks...
1. Runway centreline;
2. IAS; and
3. Engine EGTs.
So, in answer to any question about the wind vector during the takeoff roll, my answer must be "what wind vector?"
The IAS indicator will tell me anything I need to know about windshear. I don't care what the wind is. If the IAS is telling me the aircraft can't fly, then that means stop. If the IAS is telling me I can fly, and there is insufficient runway to stop, then I go. The wind might be 50 knots on the tail. I don't care. Letting a wind vector influence your stop/go judgement is asking for trouble. The aircraft doesn't care about wind, it only cares about IAS. It's IAS that makes you fly (or not), not wind. And it's the EGT's that will keep you flying... There is nothing else in the cockpit that is of any interest during the takeoff roll.
Funnily enough, Boeing don't make any mention of the wind vector in the windshear section of their manuals either. And windshear is not the only potential cause of slow acceleration: sticking brakes or incorrect takeoff data could be other examples. Only your IAS will tell you if you have slow acceleration, regardless of the cause.
So, eyes off the wind vector and back to the IAS/EGTs where they belong please folks...
HOW DOES A COMPUTER CALCULATE WIND WHEN AC IS ROLLING DOWN A STRAIGHT RUNWAY WITH NO CRAB?
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... or grant yourself the serenity to accept that just because you start a thread you don't own it. Social media has a life of it's own.
You could also accept that the question has already been asked and answered, both on this thread and the previous one... but some have trouble believing the answer...
You could also accept that the question has already been asked and answered, both on this thread and the previous one... but some have trouble believing the answer...
A_pilot, during the takeoff roll, as PIC I occasionally glance (or whatever your copy of Rogets says) at the important bits of the EWD to check if all is ok and that the PM is not asleep. It's his role (as defined in the manuals) but my responsibility at the end of the day.
1. Runway centreline;
2. IAS; and
3. Engine EGTs.
2. IAS; and
3. Engine EGTs.
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Thanks All
Wanted a technical explanation of How Its Done.
Someday when I get it, I will put it here.
Once again appreciate those who got my query.
Wanted a technical explanation of How Its Done.
Someday when I get it, I will put it here.
Once again appreciate those who got my query.
----
A_pilot:
I don't think anyone can dispute this Airbus information
Perhaps if you continued reading your document you would have discovered that your page 7 refers to windshear detection in general, not specifically during the take-off roll. For specific take-off phase windshear detection, refer to page 9, which makes no mention of the wind vector:
"Closely monitor the airspeed and speed trend during the takeoff roll to detect any evidence of windshear. "
From your earlier post:
Aren't pilots trained to gather and crosscheck information using all available resources ?
Any decision to reject a takeoff above 80/100 knots (Boeing/Airbus) due windshear is going to be based on the aircraft considered unable to fly (due insufficient IAS). There is only one instrument that can tell you this - your IAS indicator. Your wind vector is irrelevant to that decision. If you continue, stagnating IAS or speed trend is sufficient to carry out the windshear recovery. Again, your wind vector is irrelevant. Page 9 is quite clear. I seriously urge you to reconsider.
Last edited by Derfred; 12th Sep 2016 at 03:56.
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I am not entering into the last post by you because we will further divert from the present topic. In a sense we already have. From the beginning I have agreed with golden rivet's post. FOBN you quoted is an old one and I have it. I will reproduce from the same document below:
Wind shear suspected
Closely monitor the airspeed and speed trend during the take off roll to detect any evidence of wind shear.
Then again
Recovery technique for wind shear encounter during take off:
Before V1:
− Reject the takeoff only if unacceptable airspeed variations occur and the pilot assesses there is sufficient runway remaining to stop the aircraft.
And again as you quoted:
Monitor speed trend (available on the PFD, depending on the aircraft type)
Note: An unusual speed trend may be an indication of unreliable airspeed or wind shear.
Unreliable speed should lead to reject take off any way. Nowhere the document refers to wind/GS display on ND for any of these decisions.
I don't think any more discussion is required. If you have a document that says how wind direction is calculated on ground I would be interested.
Wind shear suspected
Closely monitor the airspeed and speed trend during the take off roll to detect any evidence of wind shear.
Then again
Recovery technique for wind shear encounter during take off:
Before V1:
− Reject the takeoff only if unacceptable airspeed variations occur and the pilot assesses there is sufficient runway remaining to stop the aircraft.
And again as you quoted:
Monitor speed trend (available on the PFD, depending on the aircraft type)
Note: An unusual speed trend may be an indication of unreliable airspeed or wind shear.
Unreliable speed should lead to reject take off any way. Nowhere the document refers to wind/GS display on ND for any of these decisions.
I don't think any more discussion is required. If you have a document that says how wind direction is calculated on ground I would be interested.
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aquarium1
You are not going to find how does PFD show wind but if you meant ND then read an old posts below especially post by brizeguy quoting Collins and see if those conditions are applicable on ground on take off and get your answer.
How does the ADC work out wind components ? [Archive] - PPRuNe Forums
You are not going to find how does PFD show wind but if you meant ND then read an old posts below especially post by brizeguy quoting Collins and see if those conditions are applicable on ground on take off and get your answer.
How does the ADC work out wind components ? [Archive] - PPRuNe Forums
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Hi vilas,
We agree that the wind direction displayed on the ND will be in error whilst on the ground. However the displayed nose / tail wind components will be accurate and could be used to confirm suspected wind shear during take off.
We agree that the wind direction displayed on the ND will be in error whilst on the ground. However the displayed nose / tail wind components will be accurate and could be used to confirm suspected wind shear during take off.
Last edited by Goldenrivett; 12th Sep 2016 at 08:28. Reason: typo
Dear me !
Aren't we all getting our knickers in a twist? Poor old aquarium1 was only asking HOW the wind arrow was calculated and generated on the ground - a valid question, surely?
Can I just ask - having read the archived tech link - if, as some of you seem to be saying; the wind direction arrow is not to be relied on, why do Airbus display it? It is suppressed below 100 kts, so if it was unreliable they would suppress it until V1 or Vr, or until airborne.
We had a brown trouser moment some years ago taking off from Tobago in a heavyish A330. The man in the tower either gave us the wrong wind or his equipment was faulty. There were no windsocks in our visual field. Captain said nothing between 100kts and rotate, but when we got to rotate, I rotated but nothing much happened. ROTATE shouted Captain again and I hauled on the stick. After a brief struggle, we got airborne - with a significant tailwind, (that we were not expecting).
Now, I always try to glance at the ND wind arrow at 100kts, just to make sure we are not getting a repeat of that day. It is not difficult to do - you have just looked in at your PFD to confirm 100kts, so it is not difficult to glance at the top left of the ND then outside again.
Aren't we all getting our knickers in a twist? Poor old aquarium1 was only asking HOW the wind arrow was calculated and generated on the ground - a valid question, surely?
Can I just ask - having read the archived tech link - if, as some of you seem to be saying; the wind direction arrow is not to be relied on, why do Airbus display it? It is suppressed below 100 kts, so if it was unreliable they would suppress it until V1 or Vr, or until airborne.
We had a brown trouser moment some years ago taking off from Tobago in a heavyish A330. The man in the tower either gave us the wrong wind or his equipment was faulty. There were no windsocks in our visual field. Captain said nothing between 100kts and rotate, but when we got to rotate, I rotated but nothing much happened. ROTATE shouted Captain again and I hauled on the stick. After a brief struggle, we got airborne - with a significant tailwind, (that we were not expecting).
Now, I always try to glance at the ND wind arrow at 100kts, just to make sure we are not getting a repeat of that day. It is not difficult to do - you have just looked in at your PFD to confirm 100kts, so it is not difficult to glance at the top left of the ND then outside again.
Last edited by Uplinker; 12th Sep 2016 at 13:45.
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Golden
That takes care of OP. But regarding decision making about reject due to wind shear/ UAR the airbus document points to airspeed fluctuation and trend. No where it guides you to wind display because on take off there is time constraint which is not the case once you are airborne. You don't need any confirmation from any source if there is speed and trend fluctuation because doing so may send you over V1. If the fluctuation is due unreliable speed then even more so. You can gather whatever info you want provided you have time. Notice trend fluctuation on PFD then Check wind on ND then think about what to do if it is different and it is already time to get airborne. he hasn't answered any of the things I have quoted from his documents and is thumping his back. Use of anti ice is not a split second and any one compares that with take off run then I rest my case. However you read the info from Collins that I have given and tell me about your opinion about the accuracy of wind on ground.
That takes care of OP. But regarding decision making about reject due to wind shear/ UAR the airbus document points to airspeed fluctuation and trend. No where it guides you to wind display because on take off there is time constraint which is not the case once you are airborne. You don't need any confirmation from any source if there is speed and trend fluctuation because doing so may send you over V1. If the fluctuation is due unreliable speed then even more so. You can gather whatever info you want provided you have time. Notice trend fluctuation on PFD then Check wind on ND then think about what to do if it is different and it is already time to get airborne. he hasn't answered any of the things I have quoted from his documents and is thumping his back. Use of anti ice is not a split second and any one compares that with take off run then I rest my case. However you read the info from Collins that I have given and tell me about your opinion about the accuracy of wind on ground.
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Hello
I haven't had the time to read all the topic but here are some relevant pieces of information :
- It is possible to compute the exact values of the wind if the exact values of TAS GS sideslip are known. (Obviously, you would need heading to and magnetic deviation to get the wind true direction and not only the relative direction)
- There are sideslip probes on most airbus aircraft. (Even 3 on the latest models, at least A350)
- Sideslip is valid from 60kt+
- However, TAS is not completely reliable until 100ft AGL. Under that, ground effect will induce a 2-3kt error on TAS, which will be transferred to wind calculation
However, I don't work in the ATA31 (display) department of Airbus so I have no idea when wind starts to be displayed.
However, it is calculated from 60kts+ and suffers a bit of imprecision until 100ft AGL.
Note : it is also possible to calculate the vertical wind from TAS, flight path angle (Pitch angle - average(AOA)), Vertical speed. But i'm pretty sure this is not displayed.
Which is unfortunate in my opinion.
I haven't had the time to read all the topic but here are some relevant pieces of information :
- It is possible to compute the exact values of the wind if the exact values of TAS GS sideslip are known. (Obviously, you would need heading to and magnetic deviation to get the wind true direction and not only the relative direction)
- There are sideslip probes on most airbus aircraft. (Even 3 on the latest models, at least A350)
- Sideslip is valid from 60kt+
- However, TAS is not completely reliable until 100ft AGL. Under that, ground effect will induce a 2-3kt error on TAS, which will be transferred to wind calculation
However, I don't work in the ATA31 (display) department of Airbus so I have no idea when wind starts to be displayed.
However, it is calculated from 60kts+ and suffers a bit of imprecision until 100ft AGL.
Note : it is also possible to calculate the vertical wind from TAS, flight path angle (Pitch angle - average(AOA)), Vertical speed. But i'm pretty sure this is not displayed.
Which is unfortunate in my opinion.
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Side note .. it would be such a pity were I to be moved to edit any unduly aggressive posts ... please do play the ball rather than the player, folks.
Bonjour KayPam.
On A320/A321/A330, the wind strength and direction is displayed on the ND from 100 kts on the take-off roll - I think that is IAS/TAS
Like the OP, I would be very interested to know how these older aircraft calculate the wind direction information while still on the runway, and why the wind vector information is displayed from 100 kts and not later.
Would it be possible to ask your Airbus colleagues?
On A320/A321/A330, the wind strength and direction is displayed on the ND from 100 kts on the take-off roll - I think that is IAS/TAS
Like the OP, I would be very interested to know how these older aircraft calculate the wind direction information while still on the runway, and why the wind vector information is displayed from 100 kts and not later.
Would it be possible to ask your Airbus colleagues?